1. Technical Field
The present invention relates generally to interactive computer graphics, and more specifically to achieving inverse kinematics of 3D graphics depicting how multiple parts of an object interact with each other, by using an animation of the object to build a constraint on the parts movement.
2. Description of the Related Art
Three-dimensional (“3D”) digital data may be produced by a variety of devices that involve three-dimensional scanning, sampling and/or numerical modeling. For example, computed tomography (CT) and magnetic resonance imaging (MRI) devices scan portions of a human body and generate image slices of the body, which when combined or stacked, generate a 3D representation of the body including its surface and internal volume.
Volume graphics represent a promising way to achieve the degree of realism required for high quality 3D simulations and visualization applications because volume models can contain all the surface and internal characteristics of a real object. This is in contrast to, for example, polygon-based graphics, which contain only the information about the surfaces of a 3D object. In the case of volume graphics, volume elements (i.e., “voxels”) are the base data used to represent 3D objects. Typically, voxels are simply pixels that have a third coordinate z in addition to x and y coordinates in a Cartesian coordinate system (though voxels may take various other forms, also). In other words, voxels are equally sized cubes that form a discretely defined 3D space. A typical voxel-based 3D scene can consist of one or more “voxel sets,” each of which in turn consists of one or more voxels. For example, the 3D scene may include one or more sets of MRI slices, each forming a voxel set, which in turn includes a plurality of voxels within each voxel set.
3D voxel data are rendered to produce a 2D image on a suitable output device, such as a video display or a printer. As used herein, the term “render” means to produce a 2D graphics image on an output device (e.g., a display screen) from a 3D graphics data file, and typically involves creating an image using color, texture, etc., to give the image a realistic look. In typical applications of voxel-based technologies, only one voxel set is rendered. For example, in medical MRI applications, a single voxel set representing a single MRI slice may be rendered at a time.
In other applications, such as in rendering voxel data produced using software available from NGRAIN (Canada) Corp. of Vancouver B.C., Canada, it is often necessary to render (sometimes a large number of) multiple voxel sets at a time. Briefly, NGRAIN® technology permits 3D modeling of an object, wherein each of multiple parts or layers forming the object is represented as a voxel set each consisting of one or more voxels. According to NGRAIN® technology, it is possible to render a large number of voxel sets representing multiple parts or layers together, while allowing a user to manipulate each part or layer separately in 3D space. For example, the user may break up the parts or layers to display an exploded view of an object, or to peel off an outer layer of the object to reveal its inner layer. NGRAIN® technology volume graphics are particularly suited for an interactive application to allow a user to manipulate a 3D object, for example, by rotating, resizing, or otherwise manipulating each individual part or layer of the object. Various details of NGRAIN® technology are described in commonly owned Patent Cooperation Treaty Publication No. WO 02/07088 A2 entitled “LIGHTING ADJUSTMENT METHODS AND APPARATUS FOR VOXEL DATA,” commonly owned Patent Cooperation Treaty Publication No. WO 02/07089 A2 entitled “APPARATUS AND METHOD FOR ASSOCIATING VOXEL INFORMATION WITH DISPLAY POSITIONS,” commonly owned U.S. Pat. No. 6,867,774 B1 entitled “METHOD AND APPARATUS FOR TRANSFORMING POLYGON DATA TO VOXEL DATA FOR GENERAL PURPOSE APPLICATIONS,” commonly owned U.S. Pat. No. 7,050,054 B2 entitled “METHOD, APPARATUS, SIGNALS AND CODES FOR ESTABLISHING AND USING A DATA STRUCTURE FOR STORING VOXEL INFORMATION,” commonly owned U.S. Pat. No. 7,218,323 B1 entitled “METHOD AND SYSTEM FOR RENDERING VOXEL DATA WHILE ADDRESSING MULTIPLE VOXEL SET INTERPENETRATION,” commonly owned U.S. Pat. No. 7,317,456 B1 entitled “METHOD AND APPARATUS FOR TRANSFORMING POINT CLOUD DATA TO VOLUMETRIC DATA,” commonly owned U.S. Pat. No. 7,420,555 B1 entitled “METHOD AND APPARATUS FOR TRANSFORMING POINT CLOUD DATA TO VOLUMETRIC DATA,” commonly owned U.S. Pat. No. 7,965,290 B1 entitled “METHOD, SYSTEM, AND DATA STRUCTURE FOR PROGRESSIVE LOADING AND PROCESSING OF A 3D DATASET,” and commonly owned U.S. Pat. No. 8,217,939 B1 entitled “METHOD AND SYSTEM FOR CALCULATING VISUALLY IMPROVED EDGE VOXEL NORMALS WHEN CONVERTING POLYGON DATA TO VOXEL DATA,” which are all specifically incorporated herein by reference. Additional details of NGRAIN® technology can also be found in an article entitled “Myths and Truths of Interactive Volume Graphics” published in I/ITSEC 2004 Conference.